The present invention relates generally to shaft seals and more particularly to mechanical seal assemblies of the type comprising a fixed seal housing surrounding a rotating shaft and further comprising opposed slide ring and counter ring elements one of which is attached to the shaft and the other of which is attached to the fixed housing. The ring elements rub against each other at an interface and an annular distributor guiding element defines a channel within the seal housing through which cooling and lubricating liquid is directed at said interface.
A screw type pump within the housing circulates liquid to the distributor from a seal housing inlet and increases the pressure of said liquid. After contacting the periphery of said interface, the liquid continues through an outlet channel of the housing to an exit and may be recirculated to said inlet via an external heat exchanger. The screw pump may comprise opposed cylindrical threaded surface with screw threads of opposite hand thereon, one of said surface being (for instance) an inwardly facing surface with a right hand thread affixed to the seal housing and the other surface being an outwardly facing surface with a left hand thread affixed to the rotating shaft. The two threaded surfaces are closely spaced but noncontacting.
At high and maximum circumferential speed there is the further requirement to attach the counter ring rigidly to the shaft while the axially displaceable and elastically prestressed slide ring is carried by the sealing housing which slide ring then must absorb an axial play of the shaft of, e.g., .+-. 3 millimeters and also the abrasion of the ring caused by wear. In such arrangement of the rings, the slide ring supported nonrotatably in the sealing housing must under normal operating conditions be able to execute axial motions with a travel of, e.g., 6 millimeters, which must not be hindered by the distributor guiding element connected rigidly to the sealing housing. But this implies that the distributor guiding element cannot be arranged in an optimal spatial configuration with respect to the stationary slide ring for all operating conditions and also must have such a large play with respect to the latter that the flushing out of the hot water-ring is prevented. This ring of hot coolant mixed with steam bubbles having a relatively low volume weight is formed by the influence of centrifugal forces urging cold coolant of higher volume weight radially outward to the sealing casing. In order to nevertheless achieve an adequate heat dissipation, it was necessary heretofore to increase considerably the amount of coolant conveyed in the circuit, e.g., up to values of 100 liters per minute. But a considerable power of 10 kilowatts, for example, must then be utilized to drive the pump mechanism. Apart from this undesirable waste of energy to drive the pump mechanism, this energy heating the coolant must again be removed from the coolant circuit by the heat exchanger with increased demand for cooling water. Beyond this, the dimensions of the coolant circuit are increased due to the increased volume of circulated coolant.
The object of invention is to create a mechanical sealing arrangement which at high and maximum circumferential speeds permits a reliable cooling.
It is a further object of the invention that the sealing arrangement be economical with respect to the energy demand and construction expense consistent with the preceding object.